Until recently, polyhydroxystyrenes or derivatives thereof in which the hydroxyl groups are protected with acid dissociable, dissolution inhibiting groups, which display high transparency relative to a KrF excimer laser (248 nm), have been used as the base resin component of chemically amplified resists. However, these days, the miniaturization of semiconductor elements has progressed even further, and the development of processes that use ArF excimer lasers (193 nm) to produce very fine resist patterns of 130 nm or less is being vigorously pursued.
For processes using an ArF excimer laser as the light source, resins such as polyhydroxystyrenes that contain benzene rings have insufficient transparency relative to the ArF excimer laser (193 nm).
Accordingly, resins capable of resolving this problem, which contain no benzene rings and exhibit superior levels of transparency and dry etching resistance, and which include, within the principal chain, a structural unit derived from a (meth)acrylate ester that includes a polycyclic hydrocarbon ring such as an adamantane skeleton at the ester grouping have already been proposed (see patent references 1 through 8).
Examples of this type of conventional photoresist composition include chemically amplified compositions containing a resin component obtained, for example, by radical polymerization, an acid generator component, and an organic solvent. Furthermore, in the patent reference 9, a resin is disclosed in which polymerization is conducted using a chain transfer agent that contains no polar groups at the terminals.
(Patent Reference 1) Japanese Patent (Granted) Publication No. 2,881,969
(Patent Reference 2)
Japanese Unexamined Patent Application, First Publication No. Hei 5-346668
(Patent Reference 3)
Japanese Unexamined Patent Application, First Publication No. Hei 7-234511
(Patent Reference 4)
Japanese Unexamined Patent Application, First Publication No. Hei 9-73173
(Patent Reference 5)
Japanese Unexamined Patent Application, First Publication No. Hei 9-90637
(Patent Reference 6)
Japanese Unexamined Patent Application, First Publication No. Hei 10-161313
(Patent Reference 7)
Japanese Unexamined Patent Application, First Publication No. Hei 10-319595
(Patent Reference 8)
Japanese Unexamined Patent Application, First Publication No. Hei 11-12326
(Patent Reference 9)
Japanese Unexamined Patent Application, First Publication No. 2001-2735
In recent years, the design rules required in semiconductor element production have continued to become more stringent, and improvements in resolution, such as a resolution of no more than 130 nm, and in the vicinity of 100 nm, are now being required. In addition, the occurrence of line edge roughness (LER) in the resist pattern following developing is also a problem. This LER appears as distortions around the hole patterns in a hole resist pattern, or as non-uniform irregularities in the side walls in a line and space pattern. As demands for higher resolutions grow, this LER must continue to be reduced. Furthermore, as semiconductor elements undergo ever greater miniaturization, reductions in the level of defects are also keenly sought.
However, the improvements in LER and defect occurrence provided by conventional photoresist compositions are inadequate.